1. Field of the Invention
The present invention relates to an electric joint material for an electric appliance and more particularly to an electric joint material containing silver as its primary component and a method for producing such an electric joint material.
2. Prior Art
Conventionally, electric joints produced from silver-cadomium oxide material (AgCdO), silver-tin oxide-system (AgSnO.sub.2), and silver-nickel alloy (Ag--Ni) have been used for various electric apparatus and devices such as an electromagnetic contact, relay, etc. The AgCdO or AgSnO.sub.2 system joint has been known as the joint having less fusion as well as consumption, and the Ag--Ni joint is known as the material which is less in consumption and high in workability.
However, such joints have had the problem that when they were used as the breaker joint of the type to cause an arc by means of the electromagnetic force during a short-circuit, and to split the arc by the grid to limit the electric current. In other words, because of the heavy electric current flowing during the short-circuit, the arc is caused, and the movability of this arc depends upon the joint material. The problem in the joint materials as mentioned above is that the movability of the arc is low, resulting in inferior short-circuit breakability.
Accordingly, for this type of breaker joint, it is necessary that the time between the occurrence of the arc and the entrance of the arc into the grid is short.
After repeatedly conducting various tests, the inventors found out that the joint material containing silver as the primary component with lithium oxide dispersed in the silver shows a remarkable effect in arc characteristic.
The arc stagnation time (arcing time) for the cases when various oxides are dispersed in silver is shown in Table 1. Li.sub.2 O is rated best, followed by ZnO, In.sub.2 O, Bi.sub.2 O.sub.3, in the order shown above, as seen in the Table 1.
TABLE 1 ______________________________________ ARCING TIME CONTACT MATERIAL (msec) ______________________________________ AgLi.sub.2 O (Li 1.5%) 1.2 AgZnO (Zn 3%) 1.5 AgIn.sub.2 O.sub.3 (In 3%) 1.5 AgGeO (Ge 3%) 6.0 AgBi.sub.2 O.sub.3 (Bi 0.5%) 1.5 AgSiO.sub.2 (Si 2.5%) 2.1 AgSnO.sub.2 (Sn 3%) 2.9 AgMnO.sub.2 (Mn 3%) 2.6 ______________________________________ (Short-circuit current 5.2KA)
However, when the foregoing AgLi.sub.2 O joint material is obtained by first preparing a solid material by melting silver and lithium metal in an argon atmosphere, then by further processing this solid material with an internal oxidation method wherein the solid material is left in a high temperature and high pressure oxygen gas, the grain of lithium oxide becomes coarse, and such grains tend to cohere to the grain boundary of silver. As the result, the joint formed of such joint material has the problem that it is inferior in fusion characteristic as well as in consumption characteristic.